Are 700 plus level Questions Of PS and DS are way over the limit ?

If you mean the 700-level questions on GMAT Club, some are indeed harder than any you would see on the GMAT, but most of them are not.

You can tell which are the hardest 700-level questions by using the difficulty percentage on the timer above the question. Questions marked 55% to 65% are hard but not extremely hard, questions market 75% to 85% are especially hard, and those marked 95% are the hardest of all. So, some questions marked 85% or 95% are harder than any that appear on the actual GMAT, though even some of these questions are no harder than some of the hardest ones on the test.

Also, just so you are aware, sometimes the reason a question is marked 95% is that it's flawed in some way such that almost everyone selects an incorrect choice as the correct answer.

Regarding which you should practice with, since you'll see questions of a variety of difficulty levels on the GMAT, you should practice with easy, medium, and hard questions to learn to consistently get questions of all difficulty levels correct.

For some more tips on how to prepare for GMAT quant, see the following post. How to Increase Your GMAT Quant Score: Top 25 Tips